Piezoelectric devices feature outstanding response and efficiency converting electrical energy to mechanical energy. This has resulted in the development of various piezoelectric actuators that use the piezoelectric effect of such piezoelectric devices. Piezoelectric actuators, in turn, are used in many different types of electronic devices, including piezoelectric buzzers, inkjet heads for printers, ultrasonic motors, electronic timepieces, and various kinds of mobile devices.
Piezoelectric actuators, however, use friction to drive a rotor or other driven body. As a result, even if the input energy is equal (constant), how much the driven body is driven (such as how far the rotor is turned) is not necessarily equal due to the vibration state of the oscillator and how the oscillator is engaged with the driven body (the amount of friction).
Some type of drive detection means or driven body position detection means is therefore typically used to control piezoelectric drive when a piezoelectric actuator is used.
Reference Patent 1, for example, teaches a drive detection means having a slotted plate that rotates in unison with the rotor and renders an encoder including this slotted plate and a photosensor to detect the amount of rotation (drive).
Reference Patent 2, for example, teaches a method of detecting drive by means of a switch that uses a contact spring that moves in conjunction with driving the driven body.
Reference Patent 1: Japanese Unexamined Patent Appl. Pub. 2000-199718
Reference Patent 2: Japanese Unexamined Patent Appl. Pub. 2000-56046